Method of and apparatus for burning fuel



Sept. 5, 1944.

H. J. KERR EIAL METHOD OF AND APPARATUS FOR BURNING FUEL Filed March 7,1941 4 Sheets-Sheet 1 INVENTORS Howard J. K err, James Hefc/rer, BYGeorge ,4.Wa zz:/Z0mberzM0/'stra ATTORNEY.

'Sept. 5, 1944. H. J. KERR ETIAL METHOD OF AND APPARATUS FOR BURNINGFUEL Filed March 7, 1941 4 Sheets-Sheet 2 INVENTORS Howardl Kerr, JamesFletch er, BY Gear 8/] Wait; f lambe/i Koo/515m ATTORNEY.

Sept. 5, 1944. H. J. KERR EIAL 2,357,302

METHOD OF AND APPARATUS FOR BURNING FUEL Filed March 7, 1941 4Sheets-Sheet 5 s F! g. 5

To Expansion Chambers F 5 I J INVENTORS j Howard .7. A err, limesF/ezc/ver, 54 54 5 BY George/4. Waits f Zomba/t Koo/56m WATTORNEY.

H. J. KERR EI'AL 2,357,302

METHOD OF AND APPARATUS FOR BURNING FUEL 4 Sheets-Sheet 4 Sept. 5, 1944.

Filed March 7, 1941 INVENTORS Howard J Ker/,- -Jome: flats/ref,

BY Ge rqeAM mzs I lumber! A oo/stra Q A ORNEY.

Patented Sept. 5, 1944 UNITED V STATES, PATENT OFFICE METHOD OF ANDAPPARATUS FOR BURNING FUEL Howard J. Kerr. Westfield. N. 1., and JamesFletcher, Akron, George A. Watts, Barberton, and Lambert Kooistra,Akron. Ohio. assignors to The Babcock & Wilcox Company, Newark, N. J., acorporation of New Jersey Application March I, 1941, Serial No. 382,263

The present invention relates in general to a method of and apparatusfor burning ash-con of in a inolten condition .over a relatively widerange of furnace operation.

The various features of novelty which characterize the invention are apointed out. with particularity in the claims annexed to and forming apart of this specification. standing of the invention, its operatingadvantages and specific objects attained by its use, reference should behad to the accompanying drawings and descriptive matter in which isillustrated and described a preferred embodiment of th invention.

Of the drawings:

Fig. 1 is an elevation of an experimental test installation constructedand operating in accordance with this invention; r-ziFig. 2 is a planview of the apparatus shown in Fig. 3 is an enlarged view of the cyclonefur-- the lines 6-6 and 'I-'I respectively of Fig. 5; and

Fig. 8 is an enlarged view of a portion of the furnace wall shown in Fig5.

In the experimental installation illustrated, a cyclone furnaceconstructed as hereinafter described has associated therewith suitableauxiliary apparatus for supplying controlled amounts of fuel and air tothe furnace. The auxiliary apparatus includes an air compressor havingan inlet pipe l2 and a discharge pipe I3 leading to a water heated airheater l capable of heating the air supplied to a relatively hightemperature. The preheated air leaves the air heater through a dampercontrolled air duct l6 and is divided into primary, secondary, andtertiary air streams which enter the cyclone furnace as hereinafterdescribed.

While various kinds of liquid. gaseous and solid fuels can be burned inthe cyclone furnace illus- For a better undersemi-bituminous coalshaving an ash fusion temperature below 2800 F. and reduced by crushingor pulverizati'on to an aggregate or mixture having a particle size notover Solid fuel of this character has been referred to as granular" orgranulated" fuel. The fines in the mixture passing through a 200-meshscreen should be between 3% and The minimum volatile content of the coalmay vary considerably, ranging, for example, from 20% .for a coalhavingan ash fusion temperature of 2350 F. to for a coal with an ash fusiontemperature of 2700 F. A certain percentage of fine in the mixture isdesirable to aid ignition and promote combustion of the entering fuel,but an excessive amount is undesirable as the amount of ash leaving thefurnace as fly ash is proportional- The larger the size of the coalparticles, the less the amount of fly ash, but the higher the percentageof coarse particles, the higher the air velocity required to keep theparticles in motion in the furnace. A considerattion of all of thefactors involved make a coarse fuel mixture most desirable. For example,a desirable mixture for bituminous coals having about 11% moisture, 16%ash, 39% volatiles, and a heat value of 10,300 13. t; u. per pound asfired, would be 98-100% through a 4-mesh screen, 40-50% through 30-mesh,10-18 through mesh, and 6-10% through a 200-mesh screen.

In the experimental installation illustrated, coal of the describedcharacter is supplied to a bucket elevator for delivery to a bin l8above the furnace level. The bin supplies a coal feeder I! whichdischarges the coal at; a regulable rate into a discharge pipe 2|. Thelower end of the pipe 2| extends concentrically into the rounded end ofa damper controlled primary 'air pipe 22, which is connected to the ductl6, as shown in Figs. 3 and 4. The lower end of the pipe 2| opensconcentrically into the upper end of a pipe 23 connected to the bottomof the air pipe 22. with this arrangement the primary air stream sweepsaround the lower end of the pipe 2| at a high velocity and mixes withthe descending coal stream, creating an intimate mixture of the air andcoal particles in suspension in the pipe 23. The lower portion of theair duct It extends laterally to the cyclone furnace l0, the lateralsection tapering in width towards the furnace and terminating in arelatively narrow vertically elongated nozzle secprimary air-coal spout28- positioned in spaced relation within the tapering end of the ductIS. The spout 28 tapers in width towards its discharge end which iadjacent to the discharge end of the duct nozzle section 24. Anextension arm 29 on the flange 21 permits the spout 28 to be manuallyshifted laterally about the axis of the flange 27 relative to the ductnozzle section.

In accordance with the invention, the cyclone furnance i is of axiallyelongated substantially cylindrical form and arranged with itsaxisvertical. The furnace has a substantially cylindrical casing 30 with acentral gas discharge opening in its top and a slag outlet in itsbottom. The furnace chamber 31 is defined by refractory faced fluidcooled walls enclosed by the casing and consisting of a single watertube 32, or a plurality of serially connected superposed tube coilsections, arranged in a single coil having tube portions bent to providethe various openings required in the furnace chamber. The inner side ofthe tube portions in the boundary walls of the furnance chamber havemetallic studs 34 thereon, as shown in Fig. 8, covered by a layer ofsuitable refractory 85, such as plastic chrome ore. A layer of heatinsulation material 36 is arranged between the tube coil and casing 30.The refractory-faced circumferential wall of the furnace chamber is madeas far as possible of uniform circular cross-section to avoidinterference with the flow of solids and gases through the chamber.vThis is especially important because of the helical flow path taken bythe solids and gases upwardly along the circumferential wall of thechamber in accordance with this invention.

The combustion air and fuel inlet openings are advantageously located inthe circumferential wall of the furnace chamber at positions where therewill be minimum interference with the whirling movement of the main bodyof gases moving upwardly in the chamber and the downward passage of slagin and discharge from the chamber. As illustrated in Figs. and 6,adjacent parallel tube portions in the circumferential wall are bentinto spaced overlapping groups of 180 bends 38 to define a narrowvertically elongated inlet port 89 therebetween which is tangentiallyarranged to the outer end of a section 40 of the circumferential wallshaped in the form of an involute curve extending 360 before meeting thefurnace chamber diameter. The bottom of the inlet 39 is arranged asufilcient distance above the slag outlet of the furnace chamber toavoid excessive cooling of the slag on the furnace bottom by theentering air and fuel stream. The nozzle section 24 of the duct [5 andthe air and fuel spout 28 extend into the inlet 89, as shown in Fig. 6.

With the described arrangement a narrow vertically elongated stream ofintimately mixed preheated primary air and reduced fuel particles willbe discharged at a relatively high velocity from the fuel spout 28through the inlet 39. The entering primary air-fuel stream will becompletely surrounded in the arrangement shown by a stream of preheatedsecondary air entering at a high velocity through the nozzle section 25-The combined fuel and air streams sweep horizontally along and incontact with the inner refractory faced surface of the circumferentialwall, the particular involute configuration of this portion of the wallcausing the moving stream to be wholly within the-minimum diameter ofthe furnace chamber after completing substantially one revolution, so asto minimize interference with the incoming streams from the inlet 39.The furnace draft and the displacing action of the subsequently enteringfuel and air from the inlet 39 causes the combined stream to follow ahelical fiow path upwardly along the circumferential wall after theirinitial circuit of the furnace chamber is completed.

A tertiary air supply isdelivered to the furnace chamber from the airduct l8 through a damper controlled branch connection 41 and an airinlet 4| located in the circumferential wall at a position above andangularly spaced from the inlet 29. The inlet ll is formed in the samemanner as the inlet 28 by spaced groups of overlapping bent tubeportions 42 and a. tapered nozzle section 42 at the end 01' the branchduct 48 therebetween. The inlet II is narrower and of less height thanthe inlet 38, and also arranged tangentially to the outer end of asection 44 of the circumferential wall in the shape of an involute curvesimflar to that of the wall section as shown in Fig. '7. The tertiaryair port "is angularly spaced approximately 120 in advance of the inlet39 relative to the direction of rotation of the gases in the furnacechamber. Some of the tube portions in the section 40 are bent to form aninclined inspection hole 45 in the circumferential wall.

The circular bottom or fioor of the furnace chamber is of concaverefractory, except for a downwardlytapering extension-of the tube coilat its periphery which is studded and covered with a layer of suitablerefractory. The refractory floor construction tends to increase thefloor temperature and thus aid in maintaining the slag thereon in afluid condition. The floor has a central downwardly flaring slagdischarge opening 52 therein defined by a metal cone 5! and leading to aclosed slag pit (not shown). The slag opening 5| can be closed or openedwhen desired by manually positioning or manipulating a tapered plug orgig 53 mounted on the end of an operating bar 54 which is fulcrumed on asupporting bar 54 when the plug is in the slag 40 hole.

The tube coil is continued at its upper end in a spiral to define anannular flat top section 55 and a depending concentric downwardlytapering throat 58 which forms an upwardly flaring gas outlet 51 fromthe furnace chamber. The tube portions defining the throat are studdedon both sides and covered with a layer of refractory. The throat extendsdownwardly a substantial distance into the furnace chamber, terminatingwith a minimum diameter about one-third that of the furnace chamber at alevel above the top of the tertiary air inlet 4|. The described throatconstruction results in the formation of a downwardly flaring annularpocket 58 at the upper end of the circumferential wall. open at itslower side and due to which the whirling furnace gases entering thepocket will be contracted radially and have their direction of movementaxially reversed before reaching the gas outlet 51.

The throat is extended upwardly above the furnace roof in a straightfluid cooled section formed by a bare tube coil 6|. The upper end of thecoil 6| is connected to the lower end of the throat coil, as indicatedin Fig. 5. The lower end of the coil 8| and of the peripheral fioor coilthus form opposite ends of a steam generating section, water beingsupplied at the bottom and a mixture of steam and water discharged atthe top. This circuit can be connected into the circulation system of asteam generator for which the cyclone furnace forms a source of heat. Inthe experimental illustration illustrated however, the furnace gasesleaving the throat pass out through a stack arranged above and forming acontinuation of the throat extension. The hot and removal of a highpercentage of the recoverable ash content of the fuel in a moltencondition while in the combustion zone. The cyclone furnace constructiondescribed is especially designed and particularly adapted for carryingout this fuel burning method, more particularly described hereinafter.

The total air for combustion is delivered to the air heater by thecompressor II and preheatcd to a relatively high temperature. Thepreheated air passes into the furnace as separate high velocity streamsof primary, secondary and tertiary air, the high temperature given tothe air acting to speed up ignition of the entering fuel, and the highvelocity and tangential entry of the air maintaining the desiredcentrifugal effect. The total air supply is directly proportioned to theamount of fuel supplied to the furnace, the fuel-air ratio maintainedbeing such that the total air supplied' is notmore than and preferablyless than 15%, in'excess of the theoretical combustion air requirements.The air-fuel ratio may be varied to some extent, a lower excess airratio being desirable at high fuel rates to increase the adiabat cfurnace temperature and facilitate slag tapping.

About 40% of the air supplied is used as primary or carrier air, whichintimately mixes with the coarse fuel mixture from the pipe 2| anddischarges through the spout 28. The vertically elongated primaryair-fuel stream is normally surrounded by a high velocity stream ofsecondary air from the air nozzle 24 as it enters the furnace and thecombined streams flow as a single stream horizontally along and inscrubbing contact with the involute curved wall of the furnace. Atstarting, an auxiliary oil or gas burner is inserted through one of thefurnace wall openings and after a short period of operation user toignite the solid fuel entering the furnace chamber. The air-fuel streamflows at a high velocity along the involute curved circumferential wallsection 40 and the exposure of the fuel particles to the high furnacetemperature causes them to pass rapidly through the several stages ofcombustion. Due to the location of the furnace gas outlet and thecontinuous tangential entry of air and fuel to the furnace, the burningfuel stream moves upwardly along the circumferential wall in a helicalpath.

The rapid combustion of the fuel particles results in an early releaseof the ash content thereof, and due to the centrifugal effect thereon,the sep arated ash is deposited on the furnace walls, and particularlythe circumferential wall, resulting in the formation of a thin layer orfilm of molten ash or slag which adheres to the refractory surface ofthe walls and provides a sticky surface to which fuel particles in thewhirling fuel-air stream will adhere and be burned thereon. thescrubbing action of the contacting gaseous stream aiding the rapidcombustion of the particles.

The combustion of the fuel particles in suspension and on the walls isexpedited by the introduction of the high temperature tertiary airthrough the port 4| (ill in a narrow high velocity 15 stream moving inthe same direction as and gradually merging with the rapidly rotatingair-fuel stream. The tertiary air stream intimately mixes with therising whirling stream of burning fuel, air and products of combustionand passes upwardly therewith in the helical path of flow. Combustion ofthe remaining fuel particles in suspension approaches completion as therotating burning stream reaches the upper end of the furnace chamber.With the described method of fuel and air admission to the furnacechamber and the furnace chamber construction described, the normal meantemperature therein can be easily maintained over a relatively widerange of operation substantially above the fuel ash fusion temperature.

Due to the location and configuration of the throat 56 the whirlingstream is forced to move inwardly and downwardly to reach the gas outlet51. This relatively abrupt reversal in direction of axial movement ofthe burning stream results in a further mixing of air and unburnedcombustible, effecting completecombustion of substantially all of theremaining fuel particles. This change in direction also results in anash or slag particles in suspension being thrown out of the whirlingstream and deposited on the furnace roof or outer side of the throat.The incompletely burned fuel particles will be retained in the annularpocket, either partly embedded in the slag layer on the walls thereof ormoving around in the gases therein. The particles are thus agitated andscrubbed by the gases until all of the combustible is consumed and theash content released.

The slag coating on the furnace walls rapidly reaches an equilibriumthickness which is dependent upon the velocity of the contacting furnacegases, the rate of heat absorption in the furnace walls, the ash fusiontemperature, and the furnace chamber temperature. Additional slagdeposited on the walls will flow downwardly thereon to the floor 50, theslag collecting on the floor discharging through the slag outlet 52.

With a cyclone furnace construction of the character described, i. e.with the furnace gas outlet at its upper end andthe slag outlet in thebottom. and the fuel and air for combustion entering horizontally intangential streams, it is essential that the slag flowing down thefurnace walls and on the floor should not interfere with the enteringfuel and air streams. For this reason, the inlet port 39 is located asuflicient distance above the slag hole to avoid any slag accumulationon the furnace floor reaching the inlet if the slag hole should beclosed. Any slag depositing in the inlet port would cause the flowresistance therethrough to increase and correspondingly reduce the airflow. Such accumulations in the port or on the circumferential wallwould also tend to disrupt the air and fuel flow path in the furnace anddestroy the desired high velocity whirl. With the slag flow mainly downthe minimum diameter portions of the circumferential wall and the airand fuel streams entering the furnace chamber tangentially to aninvolute wall sector extending substantially 360, the entering streamshave an opportunity of gradually merging with the whirling stream in thefurnace chamher. top and downwardly along the inner side of the incomingstreams in a shell-like formation, is minimized. The division of thecombustion air into a stream of primary and secondary air en- Theformation of slag eyebrows over the mary air, 2850 lbs. of

I had a velocity B. t. u. per cu.

tering with the fuel, and a stream of tertiary air entering at a levelsubstantially above the other stream, aids in maintaining the helicalflow path of the furnace gases and suspended particles upwardly throughthe furnace chamber. It has been found that the temperature in the lowerpart of the furnace chamber and slag temperature on the furnace bottomcan be increased when desired to increase the fluidity of the slag onthe bottom by reducing or cutting ofl entirely the secondary air supply,so that most or all of the combustion air would then be supplied to thefurnace chamber by the primary and tertiary air streams.

The relative proportions of the furnace parts, and particularly of theheight of the furnace chamber, height and diameter of the throat, anddimensions of the inlet ports 39 and ll, relative to the furnace chamberdiameter, play an important part in the operating characteristics of afurnace of this type, as described and claimed in the copendingapplication of Erwin G. Bailey -et al., Serial No. 382,262, filed March7, 1941.

By way of example and not of limitation, test runs of the. experimentalinstallation illustrated gave the following values which indicaterepresentative conditions maintained in accordance with the presentmethod. The fuel burned was Ohio No. 8 coal, reduced to the followingsize:

Per cent Through A" mesh. 99.2 Through #16 mesh 75.2 Through #50 mesh34.4 Through #100 mesh 17.6 Through #200 mesh 6.8 A proximate analysisof the coal showed Per cent Volatile matter 38.2 Fixed carbon 49.4 Ash12.4 Moisture as fired 5.0

The heat content of the coal per pound as fired was 12,600 B. t. u. At arating of 1650 lbs. of coal per hour, the total air flow was 17,500 lbs.per hour, which was divided into 7650 lbs. of prisecondary air, and 7000lbs. of tertiary air per hour. The air temperature leaving the airheater was 445 F., and the furnace temperature maintained wasapproximately 3000 F. The primary air velocity was 34,800 ft. per min.,and the tertiaryair velocity 25,900 ft. per min. The gases entering thestack of 30,500 ft. per min. The excess air was 17.4%, with a heatrelease of 680,000 ft. of furnace volume per hour. The net loss of fueldue to carryover was 0.63%. A gas analysis of the stack gases showed15.1% CO2, 3.2% Oz, and CO. About 80% of the recoverable ash content ofthe fuel was recovered in the furnace and removed through the slagoutlet in the furnace bottom and found to be free of combustible.

In another test run the same coal was burned at the rate of 919 lbs. perhour. In this run the total air flow was 10,500 lbs. per hour dividedbetween 5600 lbs. primary air and 4900 lbs. tertiary air, no secondaryair being used. The primary air velocity was 25,350 ft. per min. and thetertiary air velocity 14,800 ft. per min. The gas velocity at the stackentrance was 17,500 ft. per min. The air supply was equivalent to 21.4%excess air. The net loss due to carryover was 0.83% and the reat releaserate 381,000 B. t. u.

per cu. ft. of furnace volume per hour. An

consequence.

analysis of the flue gases showed 14.5% CO2, 3.8% 02, and 0.0% CO. Inboth of the test runs described the furnace chamber was relativelyclear, with no slag or coke accumulations of any No difficulty was hadin tapping the slag throughout substantially the entire runs.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best embodiment of the inventionnow known to us, those skilled in the art will understand that changesmay be made in the method and apparatus disclosed without departing fromthe spirit of the invention covered by our claims, and that certainfeatures of the invention may sometimes be used to advantage without acorresponding use of other features.

We claim:

1. The process of burning an ash-containing solid fuel in a furnacechamber of substantially circular cross-section having a gas outlet atits upper end and a slag outlet at its lower end which comprisesintroducing the fuel in suspension in a stream of primary air at a highvelocity directly into the lower part of the furnace chamber at a pointtangentially'to the circumferential wall thereof, burning the fueltherein to ,maintain a normal mean temperature in the furnace chamberabove the fuel ash fusion temperature, introducing air for combustion ina high velocity stream tangentially to the circumferential wall of thefurnace chamber between the point of fuel entry therein and the chambergas outlet, causing the fuel and air so introduced to move upwardlythrough the chamber in a helical path along the circumferential wall ofsufllcient length to cause the release of ash in the fuel therein andthe deposition of slag on the circumferential wall sufficient to form asticky surface thereon to which fuel particles adhere the contactinggases, and withdrawing slag separated in the furnace chamber in a moltencondition through the slag outlet.

2. The process of burning an ash-containing solid fuel at high rates ofheat release in a furnace chamber of substantially circularcross-section having a gas outlet at its upper end and a slag outlet atits lower end which comprises introducing all of the fuel in suspensionin a single stream of air at a high velocity directly into the lowerpart of the furnace chamber at a point tangentially to thecircumferential wall thereof, burning the fuel therein to maintain anormal mean temperature in the furnace chamber above the fuel ash fusiontemperature, introducing the remaining air for combustion in a singlehigh velocity stream tangentially to the circumferential wall of thefurnace chamber between the point of fuel entry therein and the chambergas outlet, causing the fuel and air so introduced to move upwardlythrough the chamber in a helical path along the circumferential wall ofsufficient length to cause the release of a high percentage of the ashin the fuel therein and the deposition of slag on the circumferentialwall sufficient to form a sticky surface thereon to which fuel particlesadhere and are scrubbed by the contacting gases, and withdrawing slagseparated in the furnace chamber in a molten condition through the slagoutlet. 7

3. The process of burning an ash-containing solid fuel at high rates ofheat release in a furnace chamber of substantially circularcross-section having a gas outlet at its upper end and a slag and arescrubbed by mary air at a high velocity directly into the lower partwofthe furnace chamber at a point tangentially to the circumferential wallthereof, burning the fuel therein to maintain a normal mean temperaturein the furnace chamber above the fuel ash fusion temperature,introducing air for combustion in a high velocity stream tangentially tothe circumferential wall of the furnace chamber between the point offuel entry therein and the chamber gas outlet, causing the fuel and airso introduced to move upwardly through the chamber in a helical pathalong the circumferential wall of sufllcient length to cause the releaseof the ash in the fuel therein and the deposition of a layer of slag onthe circumferential wall sufficient to form a sticky surface thereon towhich fuel particles adhere and are scrubbed by the contacting gases,causing the ascending gases to be deflected at the upper end of thefurnace chamber inwardly and downwardly before entering said gas outlet,and withdrawing the ash separated in the furnace chamber in a moltencondition through the slag outlet.

4. The process of burning an ash-containing solid fuel at high rates ofheat release in a vertically arranged substantially cylindrical furnacechamber having a gas outlet at its upper end and a slag outlet at .itslower end which comprises continuously introducing all of the fuel in areduced condition in suspension in a stream of primary air at a highvelocity directly into the lower part of the furnace chamber at a pointtangentially arranged relative to an involute curved portion of thecircumferential wall thereof, introducing air for combustion in a highvelocitystream tangentially to an involute curved portion of thecircumferential wall of the furnace chamber at a level between the pointof fuel entry therein and the chamber gas outlet, causing the fuel andair so introduced to move upwardly through the chamber in a helical pathalong the circumferential wall of sufllcient length to cause the releaseof a high percentage of the ash in the fuel therein and the depositionof a layer of slag on the circumferential wall suflicient to form asticky surface to which fuel particles adhere and are scrubbed by thecontacting gases, and withdrawing slag separated in the furnace chamberin a molten condition through the slag outlet.

5. The process of burning bituminous and semibituminous coals at highrates of .heat release in a vertically arranged substantiallycylindrical furnace chamber having a gas outlet at its upper end and aslag outlet at its lower end which comprises continuously introducingall of the fuel in a reduced condition in suspension in a horizontalstream of air at a high velocity directly into the lower part of thefurnace chamber tangentially to the circumferential wall thereof whilemaintaining a normal mean temperature in the furnace chamber above thefuel ash fusion temperature, continuously introducing the remaining airfor combustion in a single high velocity stream at a point tangentiallyto the circumferential wall of the furnace chamber and between the pointof fuel entry therein and the chamber gas outlet, causing the fuel andair so introduced to move upwardly through the cham ber in a helicalpath along the circumferential wall of suflicient length to cause therelease of a high percentage of the ash in the fuel therein and thedeposition of slag on the circumferential wall sufiicient to form asticky surface to which fuel particles adhere and are scrubbed by thecontacting gases, causing the ascending gases to be deflected at theupper end of the furnace chamber inwardly and downwardly before enteringsaid gas outlet, and withdrawing slag separated in the furnace chamberin a molten con dition through the slag outlet.

6. The process of burning bituminous and semi-bituminous coals at highrates of heat release in a vertically arranged substantially cylindricalfurnace chamber having a gas outlet in its upper end and a slag outletin its bottom which comprises continuously introducing all of the fuelin a reduced condition in suspension in a single high velocity stream ofpreheated air directly into the lower part of the furnace chamber at apoint tangentially to an involute curved portion of the circumferentialwall thereof and in a horizontal direction, burning the fuel therein tomaintain a normal mean temperature in the furnace chamber above the fuelash fusion temperature, continuously introducing the remaining preheatedair for combustion in a single high velocity stream tangentially to aninvolute portion of the circumferential wall of the furnace chamber at apoint between the point of fuel entry therein and the chamber gas outletand in the same angular direction as the fuel stream, causing the fueland air so introduced to move upwardly through the chamber in a helicalpath along the circumferential wall of sufficient length to cause therelease of substantially all of the ash in the fuel therein and thedeposition of a layer of slag on the circumferential wall, causing theascending streams to be deflected at the upper end of the furnacechamber inwardly and downwardly before reaching the furnace gas outlet,and withdrawing the ash separated in the furnace chamber in a moltencondition through said slag outlet.

'7. lflpparatus for burning a slag-forming fuel which comprises acombustion chamber of substantially circular cross-section arranged withits axis substantially vertical and definedby walls having an innerexposed refractory surface and fluid cooling means pioportioned topermit the maintenance of said refractory under a normal meantemperature in said combustion chamber above the fuel ash fusiontemperature, means for introducing a high velocity stream of primary airand slag-forming fuel in suspension into the lower part of saidcombustion chamber at a point tangentially to the circumferential wallof said chamber, a gas outlet at the upper end of said combustionchamber, an air inlet arranged tangentially to said circumferential wallat a location intermediate the point of fuel entry and said gas outlet,means for introducing 'air for combustion at a high velocity throughsaid air inlet in the same angular direction as the primary airfuelstream and so as to move upwardly in a helical path along saidcircumferential wall, and a slag outlet at the bottom of said combustionchamber.

8. Apparatus for burning a slag-forming fuel which comprises asubstantially cylindrical'combustion chamber arranged with its axissubstantially vertical, the circumferential wall of said chamber havingupper and lower involute curved wall sections, each of said involutecurved wall sections having a horizontal cross-sectional area enlargedrelative to the horizontal cross-sectional area of the superjacent wallsection, means for introducing a high velocity stream of primary air andslag-forming fuel in suspension into said combustion chamber at a pointat the outer end of, said lower involute curved wall section, a gasoutlet at the upper end of said chamber, an air inlet arranged at theouter end of said upper inwhite curved wall section at a locationintermediate the point of fuel entry and said gas outlet, means forintrodu g air for combustion at a high velocity through said air inletin the same angular direction as the primar air-fuel stream and so as tomove upwardly in-a helical path along said circumferential wall, and aslag outlet at the bottom of said combustion chamber below the point offuel entry.

9. Apparatus for burning a slag-forming fuel which comprises acombustion chamber of substantially circular cross-section arranged withits axis substantially vertical and defined by walls having an innerexposed refractory surface and fluid cooling means proportioned topermit the maintenance of said refractory surface under a normal meantemperature in said combustion chamber above the fuel ash fusiontemperature. means for introducing a high velocity stream of primary airand slag-forming fuel in suspension into the lower part of saidcombustion chamber at a point tangentially to the circumferential wallof said chamberand in a direction producing a helical path of travelthereof upwardly along said circumferential wall, a fluid cooled wall atthe upper end of said combustion chamber including a downwardlyprojecting throat forming a gas outlet surrounded by an annular pocket,an air inlet arranged tangentially to said circumferential wall at alocation between the point of fuel entry and said gas outlet, and a slagoutlet in the lower part of said combustion chamber below the bottom ofsaid fuel inlet.

10. Apparatus for burning a slag-forming fuel which comprises asubstantially cylindrical com-- bustion chamber arranged with its axissubstantially vertical and defined by walls having an inner exposedrefractory surface and fluid cooling means proportioned to permit themaintenance of said refractory surface under a normal mean temperaturein said combustion chamber above the fuel ash fusion temperature, thecircumferential wall of said chamber having upper and lower involutecurved circumferential wall portions, means for introducing a highvelocity stream of primary air and slag-forming fuel in suspension intosaid combustion chamber at a point tangentially to said lower involutecurved wall portion and in a direction producing a helical path oftravel thereof upwardly along said circumferential wall, a gas outlet atthe upper end of said combustion chamber, an air inlet arrangedtangentially to said upper involute-curved wall portion at a locationbetween the point of fuel entry and said gas outlet and angularly spacedfrom the point of fuel entry, means for introducing a high velocity airstream through said air inlet in the same angular direction as the fuelstream, and a slag outlet at the bottom of said combustion chamber belowthe point of fuel entry.

11. Apparatus for burning a slag-forming fuel which comprises asubstantially cylindrical combustion chamber arranged with its axissubstantially vertical and defined by walls having an inner exposedrefractory surface and fluid cooling means proportioned to permit themaintenance of said refractory surface under a normal mean temperaturein said combustion chamber above the fuel ash fusion temperature, meansfor introducing a high velocity stream of primary air and slag-formingfuel in suspension into said combustion chamber at a point tangential toan involute-shaped portion of the circumferential wall of said chamberand in a direction producing a helical path of travel thereof upwardlyalong said circumferential wall, a fluid cooled wall at the upper end ofsaid combustion chamber including a downwardly projecting fluid cooledthroat forming a gas outlet, an air inlet arranged tangentially to aninvolute-shaped portion of said circumferential wall at a locationbetween the point of fuel entry and said gas outlet, a refractory facedbottom for said chamber below the point of fuel entry, and a slag outletcentrally arranged in the bottom of said combustion chamber.

12. Apparatus for burning a slag-forming fuel which comprises asubstantially cylindrical combustion chamber arranged with its axissubstantially vertical and defined by walls having an inner exposedrefractory surface and fluid cooling means proportioned to permit themaintenance of said refractory surface under a normal mean temperaturein said combustion chamber above the fuel ash fusion temperature, meansfor introducing a high velocity stream of air and slag-forming fuel insuspension into said combus- 1 tion chamber including a narrowvertically elongated fuel inlet arranged tangentially to the outer endof an involute-shaped portion of the circumferential wall of saidchamber, a fluid cooled wall at the upper end of said combustion chamberincluding a downwardly projecting fluid cooled throat forming a gasoutlet flaring towards its upper end and surrounded by an annularpocket, an air inlet arranged tangentially to the outer end of aninvolute-shaped portion of said circumferential wall at a locationbetween the point of fuel entry and said gas outlet and angularly spacedfrom said fuel inlet, and a slag outlet at the bottom of said combustionchamber below the bottom of said fuel inlet.

13. The process of burning an ash-containing granular fuel in avertically arranged combustion chamber of substantially. circularcross-section having a fuel inlet opening at its lower end and a gasoutlet in its upper end, which comprises introducing a high velocitystream of air and fuel in suspension through said fuel inlet openinginto the combustion chamber so as to whirl about a vertical axis andmove upwardly along the circumferential wall thereof while burning thefuel to maintain a normal mean temperature in the chamber above the fuelash fusion temperature, introducing combustion air in a stream enteringat a high velocity tangentially to the circumferential wall of thecombustion chamber intermediate the fuel inlet and gas outlet thereofand in the same angular direction as the whirling streamof fuel and air,causing the fuel and air streams so introduced to merge and moveupwardly in the combustion chamber towards the gas outlet through ahelical path along the circumferential wall of sufficient length tocause substantially

